1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and particularly a semiconductor device having a conductive layer and a method of manufacturing the same.
2. Description of the Background Art
Conventional semiconductor devices are provided with conductive layers, which are formed on semiconductor substrates and serve as interconnection layers, respectively. These conductive layers can be classified into a buried type and an unburied type. In the buried type, the conductive layer is located within a groove formed in an insulating layer, and thus is buried in the insulating layer. In the unburied type, the conductive layer is formed on the surface of the insulating layer and is not buried therein.
Usually, the conductive layer buried in the insulating layer is prepared in such a manner that the groove is formed in the insulating layer, and the conductive layer is formed to fill this groove. The unburied conductive layer is formed on the insulating layer, and the conductive layer thus formed is covered with another insulating layer.
Description will now be given on a problem caused by the conventional conductive layer described above.
First, in the structure which includes the conductive layer formed within the groove at the insulating layer, the groove is usually formed by anisotropic etching effected on the insulating layer. Therefore, the side wall of the groove is substantially perpendicular to the semiconductor substrate.
In the operation of filling the groove with a conductive material, therefore, the groove cannot be completely filled with the conductive material if the groove has a large aspect ratio. This results in a so-called xe2x80x9cvoidxe2x80x9d which is a hollow portion within the conductive layer not filled with the conductive material. The presence of the void causes an open failure in interconnections, and deteriorates the reliability.
The unburied conductive layer formed on the surface of the insulating layer is formed by anisotropic etching effected on the conductive material. Therefore, the side wall of the conductive layer is substantially perpendicular to the semiconductor substrate. In the structure which includes an insulating layer covering the conductive layer thus formed, a void or hollow portion may occur in the insulating layer.
Particularly, in a structure provided with a plurality of conductive layers formed in a narrow region, the voids are likely to occur in the insulating layer filling spaces between these conductive layers, and therefore an insulation failure is likely to occur in the insulating layer.
Accordingly, an object of the invention is to provide a semiconductor device having an interconnection and overcoming the above disadvantages, and particularly a semiconductor device which allows reliable filling of a groove with a conductive material, and can improve yields in an interconnection forming step as well as a cost and a reliability.
Another object of the invention is to provide a semiconductor device, in which a conductive layer can be reliably covered with an insulating layer, and an insulation failure can be prevented.
According to an aspect of the invention, a semiconductor device includes an insulating layer and a conductive layer. The insulating layer is formed on a semiconductor substrate. The insulating layer has a concavity extending in a predetermined direction. A distance between side walls defining the concavity increases as a position moves away from the semiconductor substrate. The conductive layer fills the concavity.
In the semiconductor device having the above structure, since the distance between the side walls defining the concavity increases as the position moves away from the semiconductor substrate, the concavity can be filled with the conductive layer more easily than the case where the distance between the side walls of the concavity is constant. Accordingly, occurrence of a void (hollow portion) in the conductive layer can be prevented, and increase in electric resistance of the conductive layer can be suppressed.
Further, the width of the conductive layer filling the concavity increases as the position moves away from the semiconductor substrate. Therefore, the sectional area can be larger than that of a conductive layer having a constant width so that an electric resistance of the conductive layer can be low.
Preferably, the side wall defining the concavity has a curved surface having a center of curvature located inside the side wall. In this structure, a distance between the side walls gradually increases as the position moves away from the semiconductor substrate, and the side wall inclines gently. Thereby, the concavity defined by the side walls can be filled more easily with the conductive layer, and occurrence of the void in the conductive layer can be prevented further effectively. As a result, increase in electric resistance of the conductive layer can be prevented further effectively.
More preferably, the conductive layer and the insulating layer have top surfaces, respectively. The top surface of the insulating layer is substantially flush with the top surface of the conductive layer. In this case, a level difference is not present between the top surfaces of the insulating layer and the conductive layer, and the flatness of the semiconductor device can be improved.
Further preferably, the conductive layer is made of a single conductive material or a plurality of conductive materials.
Preferably, a bottom wall of the concavity is formed of the surface of the semiconductor substrate. In this structure, the conductive layer filling the concavity can be electrically connected to the semiconductor substrate.
More preferably, the bottom wall of the concavity is formed of a surface of a conductive region on the semiconductor substrate. In this structure, the conductive layer filling the concavity can be electrically connected to the conductive region on the semiconductor substrate.
More preferably, the concavity is formed by effecting anisotropic etching on the insulating layer.
According to another aspect of the invention, a semiconductor device includes a conductive layer and an insulating layer. The conductive layer is formed on a semiconductor substrate. The conductive layer extends in a predetermined direction. The insulating layer covers the conductive layer. A distance between side walls defining the conductive layer decreases as a position moves away from the semiconductor substrate.
In the semiconductor device having the above structure, the distance between the side walls defining the conductive layer decreases as the position moves away from the semiconductor substrate. Thereby, the insulating layer can easily cover the conductive layer. Accordingly, no void occurs in the insulating layer, and an insulation failure can be suppressed.
More preferably, the side wall defining the conductive layer has a curved surface having a center of curvature located inside the side wall. In this structure, a distance between the side walls defining the conductive layer gradually decreases as the position moves away from the semiconductor substrate, and the side wall of the conductive layer inclines gently. Thereby, the insulating layer can cover the conductive layer more easily, and occurrence of the void can be prevented further effectively. As a result, occurrence of an insulation failure can be prevented further effectively.
More preferably, the conductive layer and the insulating layer have top surfaces, respectively. The top surface of the insulating layer is substantially flush with the top surface of the conductive layer. In this case, a level difference is not present between the top surfaces of the insulating layer and the conductive layer, and the flatness of the semiconductor device can be improved.
Further preferably, the conductive layer is made of a single conductive material or a plurality of conductive materials.
A method of manufacturing a semiconductor device according to an aspect of the invention includes the steps of forming an insulating layer on a semiconductor substrate; forming a concavity extending in a predetermined direction at a surface of the insulating layer; and effecting isotropic etching on the surface of the insulating layer to process the concavity such that a side wall defining the concavity has a curved surface. The step of processing the concavity is performed to process the concavity such that a center of curvature of the curved surface is located inside the side wall. The method of manufacturing the semiconductor device further includes the step of forming a conductive layer filling the processed concavity.
According to the method of manufacturing the semiconductor device including the above steps, the curved surface is formed in the concavity by effecting isotropic etching on the surface of the insulating layer. Thereby, a distance between side walls of the concavity gradually increases as a position moves away from the semiconductor substrate. Therefore, the concavity can be easily filled with the conductive layer, and occurrence of a void in the conductive layer can be prevented. Consequently, increase in electric resistance of the conductive layer can be suppressed.
The width of the conductive layer increases as the position moves away from the semiconductor substrate, similarly to the width of the concavity. Therefore, the conductive layer can have a large sectional area. Consequently, the electric resistance of the conductive layer can be reduced.
Preferably, the step of forming the conductive layer includes the steps of depositing a conductive material filling the processed concavity and covering the insulating layer, and forming the conductive layer by removing the conductive material until the surface of the insulating layer is exposed. More preferably, the step of forming the concavity includes execution of anisotropic etching on the insulating layer.
According to another aspect of the invention, a method of manufacturing a semiconductor device includes the steps of forming a conductive layer extending in a predetermined direction on a semiconductor substrate; and processing the conductive layer to provide a side wall defining the conductive layer and having a curve surface by effecting isotropic etching on the conductive layer. The step of processing the conductive layer is performed to process the conductive layer such that a center of curvature of the curved surface is located inside the side wall. The method of manufacturing the semiconductor device further includes the step of forming an insulating layer covering the processed conductive layer.
According to the method of manufacturing the semiconductor device including the above steps, the curved surface is formed in the side wall defining the conductive layer by effecting the isotropic etching on the conductive layer. Owing to this curved surface, a distance between the side walls of the conductive layer gradually decreases as the position moves away from the semiconductor substrate. Therefore, the conductive layer can be covered more easily with the insulating layer. As a result, no void occurs in the insulating layer, and occurrence of an insulation failure of the semiconductor device can be prevented. Preferably, the step of forming the conductive layer includes execution of anisotropic etching on the conductive material.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.